<html>
<script>
  var event_count = 0;
  function callback() {
    event_count += 1;
    window.postMessage('message', '*');
  }
  window.addEventListener('message', callback, false);
  window.postMessage('message', '*');
  window.setTimeout(function() {
    console.log('Timer Fired, alot of events seen: ' + (event_count > 1));
  }, 4000);
</script>
</html>
